Protologue Description: Dirca mexicana Nesom & Mayfield, sp. nov. (Fig. 2)

Differt a Dircae occidentali A. Gray calicibus tubo longiore angustiore limbo breviore, filamentis supra medium calyces insertis, et stylis ac filamentis brevioribus.

Woody shrub 6-20 dm tall, averaging ca. 16 dm, from a single trunk branched near the base, with spreading, flexuous branches, the stems 2-3(-5) cm wide near the base of the plant, the ultimate branches 2-3 mm wide, bark smooth and grayish to reddish-brown, the current year’s growth persistently loosely and sparsely pubescent, glabrous below. Leaves deciduous, alternate, entire, at maturity broadly elliptic to slightly ovate, basally rounded, 4-8 cm long, 2.5-6.0 mm wide, 1.3-1.7 times longer than wide, the largest distally situated on the branchlets, glabrous above, the lower surface persistently sparingly strigose-sericeous on the lamina and along the veins, petioles 1-2 mm long. Buds covered by the enlarged petiole base, mixed (flowers and leaves), the apical apparently falsely terminal, the 4 bud scales whitish-sericeous, forming a foliaceous, deciduous involucre to the flowers. Flowers appearing before or concurrently with the leaves, sessile in axillary and apical fascicles, deflexed to somewhat more nodding at full anthesis, the axillary fascicles invariably producing 3 flowers, the apical fascicles sometimes apparently “twinned” with (5-)6 flowers; corolla absent, not represented by infracalycular structures; calyx (7-)8-10 mm long, petaloid, the tube narrow but slightly widening distally, 5-7 mm long, abruptly expanded into a flaring limb 2-4 mm long, the tube/limb ratio (of length) (1.5-)1.7-3.0, the 4 calyx lobes 1.5-3.0 mm. long, the lobes and limb yellow, the tube lighter yellow and drying creamy; stamens 8, filaments inserted within the calyx tube essentially at a single level (at the throat, 2.0-3.5 mm below the lobe apex), the longest exserted 2-3 mm above the calyx lobes, those inserted below the lobes 1-2 mm longer than those inserted below the sinuses, the thecae 0.4-0.8 mm long, basifixed; “hypogynous disc” or “disc” (sensu Heinig 1951) a ring of connate, irregular, slightly fleshy scales ca. 0.2-0,4 mm high and wide, basally adnate to the inner surface of the calyx base; stigma minutely capitate, above the level of the pre-dehiscent anthers on a fully elongated style, equaled or slightly surpassed by the dehiscing anthers. Fruits drupaceous, 1-seeded, pyriform to ovoid, sessile, green when young, mature fruits not observed.

TYPE: MEXICO. Tamaulipas. Municipio. Hidalgo: along mountainous road from Sta. Engracia (Tamaulipas) to Dulces Nombres (Nuevo Leon), Arroyo Obscuro, 2.0 road mi NE of Los Caballos toward Canada El Mimbre, 15.0 road mi W of lowermost crossing of arroyo El Mimbre 23?59’09”N, 99?28’37”W, ca 1800 m, 3 Mar 1995, Guy Nesom 7863 with mark Mayfield and Greg Anderson (HOLOTYPE: MEXU; ISOTYPES: AAU, ANSM, ARIZ, ASU, BH, BRIT, CAS, CHAP, COLO, CONN, DAV, DUKE, ENCB, F, FSU, FTG, GA, GH, GUADA, IEB, K, KANU, LSU, M, MICH, MO, MSC, NCU, NLU, NY, OBI, OKL, OS, OSC, P, RM, RSA, S, TENN, TEX, UARK, UAT, UC, UCR, UNL, US, VDB, WIS, WTU, XAL.
Additional collection examined: MEXICO. Tamaulipas: type locality, [sterile leaves only], 23 Sep 1994, Mayfield 2085 with Nesom (TEX).